Examination of reciprocating piston, two-stroke and four-stroke diesel cycle engine designs of previous art reveal two significant disadvantages in common.
One significant disadvantage of previous art is that during the compression stroke, the pre-compression swept volume (C) utilized to compress the air charge present to the desired maximum compression pressure is substantially the same, at best, as the expansion swept volume (E) available to subsequently expand the combustion gases during the expansion stroke, a C/E ratio of substantially 1:1. And as such, the exhaust gas temperatures and pressures of these engines are high, wasting heat energy, and further, burning the exhaust valves, a well recognized cause of engine failure.
In this respect, there have been innovations in previous art to recover or reuse the energy of the exhaust gases, but only after first discharging the gases from the combustion chamber, to drive a scavenging blower or a supercharger, as examples.
Another significant disadvantage of engine designs of previous art, a legacy of the C/E ratio of 1:1, is the necessity to commence fuel injection, initiating rapid combustion, substantially before top dead center (BTDC). Of course, in these C/E 1:1 engines, combustion must be initiated BTDC, and after top dead center (ATDC) injection/combustion is to be curtailed as the only means to prevent skyrocketing exhaust temperatures. But to initiate combustion BTDC and culminate fuel injection/combustion just when the piston literally sits at TDC is indeed a very unfortunate necessity; indeed, a very old dilemma.